Well, considering Luna and Celestia have been around for over 1000 years, we can assume Alicorns are immune to age. Normal pony races on the other hand would be hard to say. We've seen a funereal happening so we know they aren't immune to age, but apart from that there is nothing saying how long a pony lives for.
If my memory servers we rightly, I remember Granny Smith saying she was around when PonyVille was first created, which was a while ago I'd imagine. So she's probably been around for awhile. Eh, I'd probably say they have roughly the lifespan as humans. And all races probably have the same lifespans.